1. Field of the Invention
The present invention relates to a method of automatically controlling the damping force of a damper equipped in a motor vehicle dependent on the running condition of the motor vehicle and the road condition in which the motor vehicle travels.
2. Description of the Prior Art
The prior art includes known apparatus for automatically or manually adjusting the damping force of a damper to increase the riding comfort and stable maneuverability of a motor vehicle such as an automobile.
Japanese Laid-Open Patent Publications Nos. 60 (1985)-203517 and 60(1985)-209310 disclose methods of automatically controlling the damping force of a damper mounted in a motor vehicle. According to the disclosed methods, the running condition of the motor vehicle as it varies with driver's operation such as braking, steering, or motor vehicle speed is detected, and the damping force is controlled dependent on the detected running condition. Japanese Laid-Open Patent Publication No. 61(1986)-1518 shows an apparatus for controlling the damping force of a damper dependent on the road condition in which a motor vehicle runs, based on detected acceleration of vertical vibration of a motor vehicle body in addition to braking and vehicle speed.
Various mechanisms for adjusting the damping force have been employed in the above automatic control systems. In one of such adjusting mechanisms, an adjusting rod inserted through a hollow piston rod is rotated or moved upwardly and downwardly thereby to vary the cross-sectional area of an orifice through which working oil flows.
The damping force control methods disclosed in Publication Nos. 60(1985)-203517 and 60(1985)-209310 have proven unsatisfactory since the damping force is not variably controlled dependent on the road condition. While the system shown in Publication No. 61(1986)-1518 is capable of controlling the damping force dependent on the road condition by using a sensor for detecting the acceleration of vertical vibration of the motor vehicle body, the system requires many sensors and a complex control circuit inasmuch as braking and vehicle speed have to be detected in addition to the acceleration of vertical vibration.